1. By: Casey Repasy, Brenton Pedersen, Kevin McGraw, Kelsey Zdebski, and Athena Grele

2. FIRST OF ALL..WHAT IS SONAR?  Sonar, which was in itself originally an acronym for SOund Navigation And Ranging, is by definition “A method of detecting, locating, and determining the speed of objects through the use of reflected sound waves. A sound signal is produced, and the time it takes for the signal to reach an object and for its echo to return is used to calculate the object's distance…A system using transmitted and reflected underwater sound waves to detect and locate submerged objects or measure the distance to the floor of a body of water.”  It can also be referred to as echolocation, and is essentially used to navigate, communicate with, and detect other vessels

3. BEFORE SONAR…  Before sonar the only technology people used was to actually listen to the water with different devices  For example, Leonardo Da Vinci was said to have placed a tube in the water, and held his ear up to it to attempt to detect vessels in 1490 This technology (sonar) was widely impractical and seen as more of a novelty then a real science. The technology was not around because there was no use for it yet. The technology grew interest in WWI because they needed a way to detect enemy submarines.

4. THE DEVELOPMENT OF SONAR  Underwater acoustics was built upon the principles of sound observed prior to the 20th Century. It was the development of transducers in the preceding century that allowed the technique of using sound to navigate and determine the range of objects underwater to develop into the system commonly referred to as “sonar” (Sound, Navigation, and Ranging).  Until the harnessing of electricity there was no way to amplify sound, since the waves attenuate and cannot be reasonably reinforced while in motion. However, if the sound can be translated into electrical signals via the transmitters and receivers in a transducer array, the same frequency can be related with a higher amplitude, effectively increasing the volume of the sound.

5. DEVELOPMENT AND EXPLANATION CONTINUED  Little was known about the behavior of sound in water prior to transduction technology other than that it would travel at higher speeds in a liquid medium than a gaseous one. The first attempt to measure this speed was in 1808 by J. B. Biot, who literally timed how long it took sound to travel through a 1000m iron water pipe in Paris. In 1924, data detailing the dependence of sound speed on temperature, depth, and salinity was published by Heck and Service. This data served to confirm Snell’s Law as put forth by Descartes in 1637, though Snell’s Law had only previously been applied to light.  In short, when temperature, depth, and/or salinity increases, so too does the speed of sound, but because of Snell’s Law, the sound ray’s acceleration will slow and eventually bend away from the effects that are causing its speed to increase. In places where the sound can reach its maximum and minimum speeds such as the Deep Sound Channel, a layer of the ocean labeled so because sound that breaks the surface duct in two-mile deep waters runs the risk of becoming “trapped,” sound rays travel in an approximate sine wave.

6.  In 1822 Daniel Colloden used an underwater bell to find the calculations of the speed of sound underwater in Switzerland; this was a step towards sonar  In 1906 Lewis Nixon was the first to invent Sonar. He invented it to detect icebergs The picture to the right depicts it’s early and simple use

7. THE FIRST TYPES OF SONAR  The first type of sonar to detect submarines was invented in 1915 by Paul Langevin, a French Physicist This was a passive device and didn’t send out signals (he worked on the use of ultrasonic waves in submarine detection) However, by 1918 both US and Britain had active systems that sent out and received signals

8. RESULTING IMPACT OF SONAR TODAY  In the Military: Most importantly, sonar is used for navigation: using the sound waves that bounce back to navigate underwater. It is also used for Target Tracking: exactly what it sounds like; using the reflected sound waves to seek and find a target. Today the military would not be what it is if it were not for sonar; their sonar systems are very powerful, and the military would not have all of its knowledge of stealth and surveying that it has without them

9. CONTINUED IMPACT  For underwater navigation, Oceanography: Topography: sonar is used in topography to reconstruct certain shipwreck sites, underwater reefs, and certain depths of the ocean that humans and submarines cannot withstand. Animals: until sonar was discovered it was unknown how animals that dwelled in the ocean communicated with one another. Discoveries: many important discoveries of species as well as abnormalities in the ocean floor – trenches, forming volcanoes, and islands, etc.  In conclusion, sonar is a very important, successful discovery that has become extremely important and necessary for military use and under water navigation, such as oceanography and topography. Without it, our military would be put at a great disadvantage, and we would be able to do much less underwater

10. SOURCES  Rossing, Thomas D. ‘Springer Handbook of Acoustics’, Springer Science+Business Media, New York. 2007. 11-20.  http://mainland.cctt.org/istf2006/sonar.asp http://mainland.cctt.org/istf2006/sonar.asp  http://www.marinebuzz.com/2008/02/19/who-invented-sonar-a- controversy/ http://www.marinebuzz.com/2008/02/19/who-invented-sonar-a- controversy/  http://www.biologycorner.com/worksheets/articles/(article)sonar. html http://www.biologycorner.com/worksheets/articles/(article)sonar. html